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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

224                                ALASKAN GLACIER STUDIES
bottom and is in a narrow place in the fiord, though the mountain walls are the normal distance apart. Here the lower part of the glacier should erode most effectively instead of leaving a shoal. On the other hand, there are no abandoned beaches extending up to this place as in the case of the submerged moraine three miles south of it and we are not inclined to think that the irregularity represents a halt of the ice.
In the second case the upgrade of 210 feet in the southward sloping fiord bottom south of Cape Enchantment may be due to imperfect glacial sculpture of a massive conglomerate l which outcrops just here on the fiord walls. The third irregularity, at the mouth of Nunatak Fiord, rising 200 feet above the fiord bottom to the east, is also possibly explained either by glacial sculpture or as a submerged moraine, between which it is impossible to discriminate with the facts available.
The soundings made in 1910 also establish the fact that, deep as the water is, it is practically impossible that any of the glacier fronts of Disenchantment Bay and Russell Fiord are floating now and they do not seem to have been afloat at any stage of their expansion, judging by the depths of water. This means that there was always active glacial grinding on the fiord bottom and the problem arises as to where this eroded material is now. In Russell Fiord the volume, merely from the part of the fiord below sea level would be many cubic miles, and the soundings show that more material was eroded above sea level than below. Some of this material makes up the great moraine south of Russell Fiord, some is in the submerged moraines, and a great deal has gone out to sea. Some, however, doubtless remains in the fiord bottoms, making it impossible to tell how near a given sounding goes to the rock bottom, of the fiord. The measures of glacial erosion are, therefore, all minima.
In Disenchantment Bay and Russell Fiord we have no determinations of bottom material, but in outer Yakutat Bay the Coast Survey chart2 supplies some data, though not enough for a thorough study. It is evident that the sedimentary material would be chiefly clay in depths of water such as this, and the offshore slopes are such that sand should not normally be carried very far offshore. In Disenchantment Bay a section sounded in 1910 off the delta of Calahonda valley was as follows:
Distance from shore                                                                            Depth
1-8  mile.................___,.............................      12 feet
3-16   "   ....................................................    Ill "
1H,     "   ....................................................    294   "
1-2     "   ....................................................    672   "
The initial slope of the submerged delta end is at the rate of 1000 to 1200 feet to the mile, about the same as the rock surface upon which it lies.
A similar section off the delta of the Hidden Glacier stream in Russell Fiord shows a first slope at the rate of over 1500 feet to the mile, which soon flattens out.
Distance from Shore                                                                             Depth
About 100 yards.............................................        6 feet
1-8 mile......................................................195   "
1-4   "......................................................    180   "
 Tarr, R. S, and Butler, B. S., Professional Paper 64, U. S. Geol. Survey, 1909, PI. XXXV11. j Chart 8465, U. S. Coast and Geodetic Survey, 1901 and 1910.